HYDROCOLLOIDS/GUMS

• Classification based on....
  • sources
    • derivatives from exudation or sap of trees/bushes
    • extract from .....
      • seeds
      • seaweeds
      • tubers
      • plant parts
    • microbial gums
  • functional properties
    • main hydrocolloid thickeners
      • Xanthan gum
        • very high viscosity at low concentration
        • highly sheer thinning
        • maintains viscosity
          • in presence of electrolyte
          • over a broad pH range
          • temperature
      • CMC
        • viscosity
          • viscosity by addition of electrolye at low pH
      • MC & hydroxypropylcellulose
        • viscosity + temperature
          • gelation may occur
          • not influenced by addition of
            • electrolytes; or
            • pH
      • galactomannans
        • gua & locust bean gum
        • very high low-
          • shear viscosity
          • strongly shear thinning
        • x influenced by-presence of electrolyte
          • can degrade & lose viscosity
            • at high & low pH
            • when subj-->high temp.
    • main hydrocolloid gelling agents
      • Thermoreversible gelling agent
        • gelatin
          • gel forms on cooling
          • m'cules: coil-helix transition-->aggregation of helices
        • agar
          •  
          •  
        • Kappa carrageenan
          •  
            • salts; potassium salts
          •  
            • K+ bind specifically--> helices
            • salt
              • e/static repulsion <--> chains promoting aggregation
        • Iota carrageenan
          •  
          •  
        • LM pectin
          • divalent cations form gels
            • pH (3-4.5) of Ca
          • m'cules crosslinked by cations
          • pH
            • i/molecular e/static repulsion
        • Gellan gum
          •  
          • + -  
            • multivalent ions can act by crosslinking chains
          • acyl gellan gels =thermoreversible at
            • salt concentration
              • NON-thermoreversible at
                • salt content
                • divalent cations
        • MC & HMC
          • gels formed on heating
          • m'cules associate -heating due to hydrophobic interaction of methyl groups
        • Xanthan gum & locust bean gum or konjac mannan
          •  
          • xanthan & polymannan chains associate-follow xanthan coil-helix transition
      • Thermoirreversible gelling agent
        • Alginate
          • gels formed
            • addition of polyvalent cation; Ca,or
            • pH
          • m'cules crosslinked by polyvalent ion
            • guluronic acid residues give buckled up conformation providing active site for cations
        • HM pectin
          • gels formed
            • at high soluble solid content (e.g 50% sugar)
            • pH
          •  
            • e/static repulsion <--> chains
              • chain association also encouraged by
                • water activity
        • Konjac mannan
        • Locust bean gum
•  
  • range of polysaccharide & protein
  • a.k.a
    • gums
    • water soluble gums
• Functions
  • primary
    • thickening agents
    • gelling or texturizing agents
  • secondary
    • stabilization of emulsion
    • suspension of particulates
    • control of crystallization
    • encapsulation
    • formation of film